[MRCA] [Milsurplus] B+ on or off?

[Mike Feher]

Yes, I realized this a long time ago, although I just left it alone. It does
spark, but, it never seemed bad enough to destroy the contacts. I did build
a small AC supply for one of mine that fit into the battery compartment
under the receiver side. Initially, as I recall, I had the B- and one side
of the filament tied to ground. Had a lot of hum and could not initially
figure out why, till I realized I needed to separate the grounds. I had a
lot of fun with that little rig. Worked pretty much all over with it on 75
meter AM. 73 - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
David Stinson
Sent: Wednesday, December 02, 2015 7:39 AM
To: milsurplus at mailman.qth.net; mrca at mailman.qth.net;
boatanchors at theporch.com
Subject: Re: [Milsurplus] B+ on or off?

(Copied to the mil lists for information)

Just in case anyone has a BC-474 in the stacks:
There is a B+ related design flaw in the set.
An electrolytic on the B+ lead smooths the generator output in transmit.
It's connected *after* the TX/RX rotary switch B+ switching contact.  As a
result, when one switches to TX, B+ surges to charge the cap and sparks at
the switch contact, hot enough to vaporize some of the contact. 
If continued, it will destroy the switch.  
The cure is to disconnect the cap or move the connection to the other side
of the switch.

73 DE Dave AB5S

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